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APPLICATION OF THE LAWS OF HYDROSTATICS 11
Just as a river has a depth which is a function of the volume
of water flowing, it is evident that a stream of gases will have a
thickness which is a function of the volume of gases flowing. If,
on this basis, water is used to simulate the cold air and colored
kerosene to simulate the hot gases flowing in the flue, it would not
be difficult to show a smoke flue filled or partially filled with a
stream of kerosene. This demonstration is considered useless
as it has been thoroughly established that flowing streams of hot
gases do not require anything to confine their lower surface and
that the thickness or depth of the stream is a function of the
volume of the gases which are flowing.
Therefore, when currents of hot gases are dealt with, they will
always be represented as inverted streams of water.
IV. APPLICATION OF THE LAWS OF HYDROSTATICS TO HOT
The weight per cubic meter of the products of combustion of
the ordinary combustibles varies from 1 kg 29 to 1 kg 33 at 0°
and 760 mm. The computations may be simplified, and will be
sufficiently exact, if the first of these values is assumed as the
weight of the products of combustion, because this value is also
the weight of a cubic meter of air. At any temperature t the
weight of 1 cu m of the hot gases will be, therefore, /' ' kg, in
which a = = 0.00367.
By reason of this large coefficient of expansion of gases, the
difference between the weight of a cubic meter of atmospheric air
(1 kg 29) and a cubic meter of the gases of combustion, taking,
for example, those in an open-hearth furnace (0 kg 17) is quite
large, being equal to 1.29—0.17 = 1 kg 12. It is this difference
between the weight of the air and the weight of the flame or hot
gases which causes the hydrostatic pressure of the latter.
The following experiments will serve to make this clear (Fig. 9).
The upper surface of the water in a beaker is at aa; and B is a
lamp chimney into which kerosene has been poured until its
lower surface is at the bottom of the lamp chimney. It can be
seen that the upper surface of the kerosene 66 in the lamp chim-
ney is higher than the surface of the water in the beaker.
The difference in level between aa and 66 can be computed in